Biological stressors and systemic markers of oxidative stress: The effect of prolonged hypergravity and isolation on autonomic regulation and oxidative stress in humans

This study was designed to examine whether 5 biochemical markers of oxidative stress rose in response to a biological and psychological stressor: Sustained hypergravity and isolation. Four adult subjects were recruited from a healthy population. Following a baseline familiarization run, each subject underwent 22-hour exposure to 1.0 and 1.25 times earth's gravity in the 20-G centrifuge at NASA Ames Research Center. One subject underwent additional 22-hour exposure at 1.5 times earth's gravity (1.5 G). Serial urine specimens were collected during each of the centrifuge runs and analyzed for 5 biochemical markers of oxidative stress. Included were 8-epi-PGF2α (F2 Isoprostanes), lipid hydroperoxides, aqueous hydroperoxides, total alkenals (MDA, 4-HNE), and 8-hydroxy-2-deoxy-guanosine. Baseline, mid-point, and end-point measures were compared.; This study revealed that 22-hour centrifugation of human subjects does not produce significant, linear changes from baseline to endpoint in urinary levels of 8-epi-PGF2α, lipid hydroperoxides, aqueous hydroperoxides, total alkenals (MDA, 4-HNE), and 8-hydroxy-2-deoxy-guanosine at 1.0 and 1.25 G. However, 22-hour centrifugation of human subjects at 1.5 G (n = 1) results in increased oxidative stress reflected by changes in 8-epi-PGF2α, lipid hydroperoxides, aqueous hydroperoxides, and total alkenals (MDA, 4-HNE). Additionally, at 1.5 G, the single subject experienced nausea concomitant with a rise in 8-epi-PGF2α, which was followed by emesis that was associated with a fall in 8-epi-PGF2α. It is hypothesized that hypoxia may lead to formation of the oxidative product of arachidonic acid degradation, 8-epi-PGF2α, and its isomeric counterpart, PGF2α, which act as smooth muscle agonists to produce changes in gastrointestinal smooth muscle motility. Thus, a new mediator of motion sickness symptoms may have been identified along with elucidation of a new hypothesis suggesting an underlying mechanism for several other conditions that have nausea and vomiting as associated symptoms such as high altitude sickness, migraine, and various conditions associated with pregnancy. The effects of biological stressors and oxidative stress on the brain and nervous system were examined.